Location tracking method in coordinator-based wireless network

ABSTRACT

A location tracking method in a coordinator-based wireless network is provided. The location tracking method in a coordinator-based wireless network includes transmitting a first frame including its own identifier and time information to the wireless network by a device associated with the wireless network in order to disclose its location information; and receiving a second frame including the location information of the device transmitted from the wireless network by the device, as a response to the first frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application Nos.10-2004-0058263 and 10-2004-0086226 filed on Jul. 26, 2004 and Oct. 27,2004, respectively, in the Korean Intellectual Property Office, thedisclosures of which are incorporated herein by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Methods consistent with the present invention relate to locationtracking in a coordinator-based wireless network.

2. Description of the Related Art

A recent trend in networking is to interconnect devices that need toexchange data, in addition to computers. In the past, wired networkingwas the norm. But, the disadvantages of the wired networking, such aswiring construction and limited mobility, necessitate wirelesscommunication technology. Wireless Local Area Network (WLAN) andWireless Personal Area Network (WPAN) standards are being developed. AWPAN has a range of 10 m, while WLAN has a range of 50 m to 100 m. TheWPAN is more suitable for electronic home appliances in terms ofmobility and range because it consumes less power and supports Ad-hocnetworking.

The coordinator-based wireless network uses a coordinator to manage thecommunication time and competition mode of the wireless network. It usesmany of the protocols decided by IEEE 802.15 working group, which wasfounded to establish a WPAN standard. The IEEE 802.15 working group isdivided into four task groups. TG 1 works on the standards for WPANbased on Bluetooth 1.x. TG 2 studies co-existence of the wirelessnetworks. TG 3 studies Ultra Wideband (UWB), which provides a hightransmission rate of 20 Mbps or more with low power consumption. TG 4studies Low Rate WPAN (LR-WPAN), a technology to provide a lowtransmission rate (maximum 250 kbps) at a low power consumption.

LR WPAN is concerned with low-cost communication networks that requirelow data transmission rates. The IEEE 802.15.4 standard known as“ZigBee” is a wireless transmission technology for networks of low cost,low power devices such as wireless integration remote controllers, homeappliance controllers, building management controllers and toys. TheZigBee group was established in July, 2000 and since then it hasfinished working on the standards for the physical layer and MAC.

The standard specifies that the transmission is 250 kbps (16 channels inthe 2.4 GHz band) or 40 kbps/20 kbps (10 channels in the 915 MHz band orone channel in the 868 MHz band), and the range is 1 m to 100 M.

Work is still being done on the upper layer, which includes a networklayer. Fifty companies including Philips, Motorola, Honeywell,Mitsubishi, Invensys, and Samsung are promoters in a ZigBee Alliance inorder to supplement the existing standard by adding ad-hoc wirelessnetworking and a network protocol for dispersed devices.

ZigBee does the job of preparing check lists and specifically definingapplications to practically perform the interoperability test. Therequirements of IEEE 802.15.4 include low power consumption, low cost,and simple infrastructure. These requirements are necessary to networksensors and control devices.

IEEE 802.15.4a defines the standard for a low-rate location-basednetwork using Ultra Wideband (UWB), which is a new networking technologyimplementing a precise location awareness service making a ubiquitousenvironment achievable.

IEEE 802.15.4a is a subgroup of 802.15.4 and it uses the same MediumAccess Control (MAC) as 802.15.4, but substitutes UWB for the PhysicalLayer (PHY). But, it does not define a location tracking protocol. So, alocation-based service has to be added to the coordinate-based wirelessnetwork to embody the location tracking technology of IEEE 802.15.4a. Aprivacy protection service should also be added in a manner that allowsa user control over the location tracking.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a location trackingfunction in a coordinator-based wireless network.

Another aspect of the present invention is to track the location of adevice based on a wireless communication technology such as UWB by usingthe location tracking function of the coordinator-based wirelessnetwork.

The aspects of the present invention are not limited to theabove-mentioned aspects and other aspects which are not mentioned willbecome more apparent from the below description by those of ordinaryskill in the art.

The present invention provides a location tracking method in acoordinator-based wireless network. The location tracking method in acoordinator-based wireless network according to one exemplary embodimentof the present invention comprises transmitting a first frame includingan identifier and time information to the wireless network by a deviceassociated to the wireless network in order to disclose its location;and receiving a response frame including the location information of thedevice transmitted from the wireless network.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisestransmitting a first frame including identifiers of a first device and asecond device to the wireless network so that the first deviceassociated to the wireless network becomes aware of the location of thesecond device; and receiving a response frame including locationinformation of the second device transmitted from the wireless networkby the first device.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier of a first device whichrequests location tracking of a second device and an identifier of thesecond device from the wireless network by the second device; andtransmitting a second frame including the identifier of the firstdevice, the identifier and the time information of the second device tothe wireless network by the second device, as the response of the firstframe.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier of a first device whichrequests location tracking of a second device, and an identifier of thesecond device from the wireless network by the second device;determining whether location tracking is allowed; and if locationtracking is allowed, the second device transmits a second frameincluding the identifier of the first device, and the identifier and thetime information of the second device to the wireless network, as theresponse to the first frame.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier and time information ofa device transmitted by the device; obtaining location calculatinginformation used in calculating the location of the device using thetime information; and transmitting a second frame including theidentifier of the device and the location calculating information to anetwork coordinator.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier of a first device whichrequests location tracking of a second device, an identifier and timeinformation of a second device transmitted by the second device;obtaining location calculating information used in calculating thelocation of the second device using the time information; andtransmitting a second frame including the identifier of the firstdevice, the identifier of the second device and the location calculatinginformation to a network coordinator.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a plurality of frames including an identifier of a device andlocation calculating information of the device from the network;calculating the location of the device using the location calculatinginformation; and transmitting a frame including location information tothe device.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a plurality of frames including an identifier of a firstdevice which requests location tracking of a second device, anidentifier and location calculating information of a second device froma network; calculating the location of the second device using thelocation calculating information; and transmitting a frame including thelocation of the second device to the first device.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier of a first device whichrequests location tracking of a second device, and an identifier of asecond device from a network; transmitting the first frame to the seconddevice of the network; receiving a second frame for notifying thatlocation tracking has been denied from the second device; andtransmitting the second frame to the first device.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier of a first device and anidentifier of a second device transmitted by the first device so thatthe coordinator of a first wireless network can track the second device;transmitting a second frame including an identifier of the firstwireless network, the identifier of the first device and the identifierof the second device to the coordinator of a second wireless network bythe coordinator of the first wireless network; receiving a third frameincluding the identifier of the first wireless network, the identifierof the first device, the identifier of the second device and thelocation information of the second device transmitted by the coordinatorof the second wireless network, by the coordinator of the first wirelessnetwork, as the response to the second frame; and transmitting a fourthframe including the location information of the second device to thefirst device by the coordinator of the first wireless network.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier of a first device and anidentifier of a second device transmitted by the first device so thatthe coordinator of a first wireless network can track the second device;transmitting a second frame including the identifier of the firstwireless network, the identifier of the first device and the identifierof the second device to the coordinator of a second wireless network bythe coordinator of the first wireless network; receiving a third frameincluding the identifier of the first wireless network, the identifierof the first device, the identifier of the second device by thecoordinator of the first wireless network, as the response of the secondframe, if the second device which received the second frame denieslocation tracking; and transmitting a fourth frame including theinformation that the second device denies location tracking to the firstdevice by the coordinator of the first wireless network.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier of a first wirelessnetwork, an identifier of a first device which requests locationtracking of a second device, and an identifier of a second devicetransmitted by the coordinator of the first wireless network, by acoordinator of a second wireless network; transmitting a second frameincluding the identifier of the first wireless network, the identifierof the first device and the identifier of the second device to thesecond device associated with the second wireless network by thecoordinator of the second wireless network; receiving a plurality ofthird frames including the identifier of the first wireless network, theidentifier of the first device, the identifier of the second device andlocation calculating information of the second device from the secondwireless network by the coordinator of the second wireless network;calculating the location of the second device using the locationcalculating information of the second device by the coordinator of thesecond wireless network; and transmitting a fourth frame including theidentifier of the first wireless network, the identifier of the firstdevice, the identifier of the second device and the calculated locationinformation of the second device to the coordinator of the firstwireless network by the coordinator of the second wireless network.

The location tracking method in a coordinator-based wireless networkaccording to an exemplary embodiment of the present invention comprisesreceiving a first frame including an identifier of a first wirelessnetwork, an identifier of a first device which requests locationtracking of a second device, and an identifier of a second devicetransmitted by the coordinator of the first wireless network;transmitting a second frame including the identifier of the firstwireless network, the identifier of the first device and the identifierof the second device to a coordinator of a third wireless network by thecoordinator of the second wireless network; receiving a third frameincluding the identifier of the first wireless network, the identifierof the first device, the identifier of the second device and thelocation information of the second device transmitted by the thirdwireless network, by the coordinator of the second wireless network; andtransmitting a fourth frame including the identifier of the firstwireless network, the identifier of the first device, the identifier ofthe second device and the location information of the second device tothe coordinator of the first wireless network by the coordinator of thesecond wireless network.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 illustrates the structure of a cluster-tree network of 802.15.4according to an exemplary embodiment of the present invention;

FIG. 2 is a flowchart illustrating the process which a tracked devicerequests the self location awareness to a coordinator according to anexemplary embodiment of the present invention;

FIG. 3 is a flowchart illustrating the process which the coordinatorrequests the remote location awareness to the tracked device accordingto an exemplary embodiment of the present invention;

FIG. 4 is a flowchart illustrating the process which the device otherthan a PAN coordinator or a cluster header requests the locationtracking of the other device according to an exemplary embodiment of thepresent invention;

FIG. 5 is a flowchart illustrating the process for tracking the locationof the tracked device which exists at the outside of the cluster inwhich the PAN coordinator exists according to an exemplary embodiment ofthe present invention;

FIG. 6 is a flowchart illustrating the process for tracking the locationof the tracked device which exists at the outside of a relay deviceaccording to an exemplary embodiment of the present invention;

FIG. 7 is a concept diagram illustrating the location tracking by a TOAmethod according to an exemplary embodiment of the present invention;

FIG. 8 illustrates the structure illustrating the location tracking bythe TDOA method according to an exemplary embodiment of the presentinvention;

FIG. 9 illustrates a frame format of an MAC layer for embodying alocation tracking function according to an exemplary embodiment of thepresent invention in 802.15.4; and

FIGS. 10, 11, 12 are block diagrams illustrating command payloads of aframes according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

Terminology used in the specification will be described in thefollowing.

Coordinator-Based Wireless Network

A network including a wireless network device functioning as acoordinator (hereinafter, referred to as coordinator-based wirelessnetwork) forms a single independent wireless network on the basis of thecoordinator. If pluralities of coordinator-based wireless networks existin the same area, each coordinator-based wireless network has a uniqueidentification that distinguishes it. The coordinator-based network isdifferent from an infrastructure network for performing wirelesscommunication through an access point or a base station, and it mayinclude a plurality of coordinators and be included in an ad-hocnetwork. The coordinator can transmit time information required for awireless network, and the wireless network devices that receive thisinformation can transmit it to other network devices. In thisspecification, an IEEE 802.145.4 coordinator-based wireless network willbe described, but this is only an exemplary embodiment of the presentinvention and the present invention is not limited to this.

Beacon Frame

The beacon frame notifies of the existence of a network and it alsoperforms an important role in the maintenance of the network. The beaconframe includes a payload that is required when network devices associatewith the network. The network coordinator periodically transmits thebeacon frame so that a device participating in the wireless network canrecognize the network.

Probe Request

The probe request frame is sent by a network device to find a network.

Probe Response

The network coordinator which receives the probe request from thenetwork device transmits a probe response frame which sets informationrequired when the device associates with the network.

Device, Network Device

The device is a component of the wireless network that can communicatewith other devices. For example, in IEEE 802.15.4, in addition to thewireless integration remote controller and the electronic home appliancecontroller, there is a building management controller, a toy, a mouse,and a cooker. A device having a communication function, a controllingfunction and a sensor function in a home network or a ubiquitousenvironment is also included.

Location Awareness Frame

The location awareness frame allows both the network device and otherdevices to know its location. The other devices that receive thelocation awareness frame can become aware of the location of the networkdevice through a location tracking algorithm. The location awarenessframe may include the time of transmission of the frame, an identifierof the seeking device, and an identifier of the device that is theobject of the location tracking.

Location Information Positioning Frame (Location Calculating InformationFrame)

The location information frame includes the location of the device,which is calculated using the frame transmission time and the framereception time, the angle of the received signal including the frame orthe received signal strength. The location may be expressed as a timedifference; that is, the difference between the frame transmission timeand the frame reception time.

Location Result Frame

The location result frame includes the location information obtained bya specific device that receives the location information frame (thelocation calculating information frame). This frame may be transmittedto a device that wants to know its own location.

Location Awareness Request Frame

The location awareness request frame is to request the transmission ofthe location awareness frame so that a device located outside thecluster can know the location of a specific device. The locationawareness request frame can be transmitted by a cluster coordinatorlocated outside the cluster or by a coordinator located inside thecluster. In addition, the location awareness request frame can betransmitted by a device located inside or outside the cluster, which caninsert its identifier in the frame.

FIG. 1 illustrates the structure of a cluster-tree network of 802.15.4according to an exemplary embodiment of the present invention. 802.15.4includes the star, peer-to-peer, and cluster-tree topology which is amodification of peer-to-peer topology.

The star topology is shown by reference numeral 20 of FIG. 1 and has onenetwork coordinator 21. The communication between the network devices isperformed by this coordinator, and a full function device (FFD) and areduced function device (RFD) can participate in the star topology. Thefull function device can communicate with other network devices and canact as the network coordinator. The reduced function device cancommunicate only through the network coordinator. The reduced functiondevice cannot become the network coordinator, since it cannotindependently communicate with other devices.

Reference numeral 10 of FIG. 1 shows a peer-to-peer topology having onenetwork coordinator. Devices can communicate with the other devices inthis type of network. The above-mentioned reduced function device cannotparticipate in a peer-to-peer network.

The cluster-tree network is the modification of the peer-to-peertopology and it may integrate several networks (e.g., 10, 20, and 30).It is composed by associating at least two networks. Each network iscalled a cluster. In FIG. 1, there are three clusters 10, 20, 30 and thenetwork coordinators of these clusters are labeled 11, 21, and 31,respectively. The network coordinator of the cluster is called a clusterheader. The coordinator 31, which is a PAN coordinator, for coordinatingthe cluster-tree network can be determined among the networkcoordinators. It may be preferable that the PAN coordinator 31 has morecomputing capability and resources than the other network devices. Thedevice passing through the network of FIG. 1 can communicate with thenetwork devices in the corresponding cluster according.

Location awareness can be largely divided into two cases. In the firstcase, the network device requests location awareness from the PANcoordinator or the cluster header in order to know its location. In theother case, the PAN coordinator or the cluster header requests thelocation of the network device. The former is referred to as a selflocation awareness request and the latter is referred to as a remotelocation awareness request.

For convenience of explanation, hereinafter, the network device that hasits location tracked is referred to as a tracked device and the networkdevice that receives the location tracking information from the trackeddevice is referred to as a reference device.

FIG. 2 is a flowchart illustrating the process where a tracked devicerequests the self location awareness from a coordinator according to anexemplary embodiment of the present invention. In FIG. 2, the trackeddevice 101, which participates in the cluster, requests locationawareness in order to know its location, and the PAN coordinator or thecluster header serves as the coordinator. A cluster is a portion of thenetwork in FIG. 1, but it can be the entire network if there is only onecluster. Among various topologies of IEEE 802.15.4, cluster-tree network(the most complicated topology) is illustrated in the presentspecification, but the star or the peer-to-peer topology may be applied.

FIG. 2 shows the active scanning process. The coordinator 31continuously transmits a beacon frame (S101). However, the trackeddevice 101, which has not received the beacon frame, transmits a proberequest frame in order to notify that it wants to participate in thenetwork (S103). The coordinator 31 becomes aware that a device wants toparticipate in the network and transmits a probe response frameincluding the network information (Si04). The tracked device 101 obtainsthe information required for network association through the receivedprobe response frame and transmits an association request frame (S107).The coordinator 31 transmits an association response frame, which setsthe information required for the association, to the tracked device(S108). Hereafter, the tracked device can communicate with the network.The tracked device associated to the network transmits a self detectinitiation frame in order to search its location (S115). This frame isreceived by reference devices 301, 302 and the coordinator 31 (the PANcoordinator or the cluster header). Using the received signal strength(RSS) of the frame and the time information included in this frame, theposition of the tracked device can be calculated. The reference devices301, 302 transmit positioning data to the coordinator 31 (S121) and thecoordinator 31 calculates the location using this data and the locationtracking algorithm. If the coordinator 31 transmits a self detect resultframe including the location value to the tracked device 101 (S150), thetracked device 101 becomes aware of its location. Then, if the trackeddevice 101 is moved, it can become aware of its location throughoperations SI 15 to SI 50, because it is associated with the network.The location tracking algorithm will be explained in the following.

The difference between the reference device and the tracked devicedepends on whether it is the object to be tracked. Accordingly, sincethe tracked device 101 became aware of its location, it can now become areference device. In case that another device participates in thenetwork, the tracked device 101 can act as a reference device andreceive the location information of the other device. Also, even whenthe device 101 acts as a reference device, a new location thereof may beascertained through operations 115 to 150, if the device 101 is moved.That is, although the device is a reference device, it may become thetracked device again. The difference between the reference device andthe tracked device depends on whether it is the reference forascertaining a device location or the object to be tracked.

FIG. 3 is a flowchart illustrating the process where the coordinator 11requests the remote location awareness according to the other exemplaryembodiment of the present invention. FIG. 3 shows an example of apassive scanning process where the network coordinator searches for thetracked device and transmits the information. A new network device islabeled a tracked device 102, in order to distinguish from the othernetwork devices. The coordinator 11 continuously transmits a beaconframe in order to maintain and manage the network (S201). The trackeddevice, which becomes aware of the existence of the network by thebeacon frame, transmits an association request frame (S207). If thecoordinator 11 transmits the association response frame accepting theassociation request (S208), the tracked device 102 can communicate withthe network.

The coordinator 11, which has associated the tracked device with thenetwork, transmits a detect call request frame in order to know thelocation of the tracked device (S211). The detect call request frame isdifferent from the self detect initiation frame of FIG. 2. In order toensure privacy, whether the tracked device 102 allows location trackingis determined in operation S212. When the tracked device 102 allowslocation tracking, it transmits its location information to thecoordinator and the peripheral devices.

The tracked device 102 transmits the detect call response frame, whichcontains its network identifier and a timestamp, so that its locationcan be known (S215). The reference devices 401, 402 and the coordinator11 which receive this frame positions the location and the related dataof the tracked device by the information such as the received signalstrength (RSS) of the frame and the time information included in thisframe. The reference devices 401, 402 transmit this positioning data tothe coordinator (S221) so that the coordinator 11 can calculate thelocation of the tracked device 102 using the location trackingalgorithm.

When the tracked device 102 does not allow location tracking, thetracked device 102 transmits a detect call deny response frame to thecoordinator 11 and the peripheral devices (S216).

The location information is important for network management.Accordingly, the coordinator 11 needs to know the location informationof the devices composing the network or the cluster, although everydevice need not know the location information. Accordingly, the PANcoordinator or cluster header can get the location information of thedevices according to the network configuration, though the device deniesnotifying its location.

When the location information is sent to both the PAN coordinator 31 andthe cluster header 11 (case 1) the detect call deny response frame istransmitted (S216). When the location information is forcibly sent toonly the PAN coordinator 31 (case 2) the tracked device cannot transmitthe detect call deny response frame and the detect call response frame.

In case 2, there is a method for unconditionally transmitting the detectcall response frame; that is, without asking the user whether he/sheallows location tracking. For convenience of explanation, the method fortransmitting the detect call response frame without user permission willbe explained in the following.

When the coordinator that transmits the detect call request frame is thecluster header, the cluster header cannot obtain the locationinformation of the other device, because only the PAN coordinator canforcibly obtain the location of the device. This is because the clusterexists only for a certain time. Accordingly, in case that the trackeddevice 102 denies notifying its own location, the detect call denyresponse frame is transmitted to the cluster header 11 and the referencedevices 401, 402 (S216), and the process halts. When the locationinformation is forcibly sent to the PAN coordinator and the clusterheader the tracked device 102 cannot deny the detect call request. Thelocation of the device is notified to the coordinator, regardless ofuser permission. As such, for user convenience, the process can progressto operations S215 to S221.

Operation S212 of FIG. 3 is optional. If the network can forcedly knowthe location between the devices, the process progresses, whether thetracked device allows or denies location tracking. If the tracked device102 is forced to allow location tracking, the process is progresses tothe operation where the tracked device transmits the detect callresponse frame, without transmitting the message that asks forpermission. At this time, only operations S201 to S221 are performed.The location information may be transmitted to the coordinator even ifthe user denies location tracking, but it is varied according to theallowance or denial of the user.

On the other hand, for the sake of convenience, the user can previouslyset the response of the tracked device 102. For example, when the devicethat requests location tracking is the coordinator, the detect callresponse frame can be set to be unconditionally transmitted. Theresponse may be set such that the tracked device 102 allows every deviceor only devices in the cluster to which it belongs to track itslocation. After the response is set, the detect call response frame istransmitted to only the allowed device or the coordinator, and thedetect call deny response is transmitted to all other devices, withoutuser input. The location tracking method of FIG. 3 includes privacyprotection. Accordingly, operations S212 to S216 may be omittedaccording to the structure of the network.

FIGS. 2 and 3 show the process for participating in the network and forobtaining the location of the tracked device 102. The process of FIG. 2for actively associating with the network the device that requests selflocation awareness is not necessarily performed. The self detectinitiation frame can be transmitted after the tracked device isassociated with the network by the passive scanning of FIG. 3. On thecontrary, even after the active network scanning of FIG. 2, thecoordinator may transmit the detect call request frame in order to knowthe location of the tracked device 102. Also, the reference device canbe a relay device that receives the frame for establishing the locationof the tracked device, and sends the location information contained inthis frame to the cluster header.

FIG. 4 is a flowchart illustrating the process where a device other thana PAN coordinator or a cluster header requests location tracking of athird device according to an exemplary embodiment of the presentinvention. In addition to FIGS. 2 and 3, additional operations may beneeded. Since tracking the location of the other device may infringeuser privacy, a location tracking request can be sent. The referencedevice 401 can request location tracking of the device 102. At thistime, the device 401 can include its identifier and request theidentifier of the tracked device in the frame (S251). The coordinator(the cluster header) 11 receives the detect call request frame andtransmits it to the tracked device 102 (S252). The tracked device 102becomes aware that the reference device 401 wants to track its location.A message such as: “A device 401 requests location tracking. Will youallow location tracking?” may be displayed to the user of the trackeddevice 102. If the user sees the message and allows location tracking,the frame including the time information for tracking its own location(detect call response frame) is transmitted (S255). The referencedevices 401, 402 receive the detect call response frame, calculatepositioning data and transmit this data to the coordinator (the clusterheader) 11 (S257). The coordinator 11 then transmits the locationinformation of the tracked device 102 to the reference device 401(S260).

However, when the user does not allow location tracking in operationS253, the device 102 transmits the detect call deny response frame tothe coordinator 11 and the reference devices 401, 402 (S256).

In FIG. 4, the information on whether the user of the tracked device 102allows or denies the detect call response frame can be previously set,and it can be set for every device or for specific device(s). By thissetting, the user can maintain his/her privacy, without having torespond to location tracking queries.

FIG. 5 is a flowchart illustrating the process of tracking the locationof a tracked device that exists outside the cluster that the PANcoordinator resides in according to an exemplary embodiment of thepresent invention. The embodiment of FIG. 5 includes the case where thePAN coordinator 31 requests the location of the tracked device 102, andthe case where another device requests the location of the trackeddevice 102.

The PAN coordinator 31 transmits the detect call request frame to thecluster headers 11, 21 in operation S311 in order to track the locationof a specific device. The PAN coordinator 31 can also receive thelocation tracking frame transmitted by the cluster header CLH1 21 andtransmit it to the whole network. The cluster header 11 which receivesthis frame transmits the detect call request frame in order to know ifthe tracked device exists in its cluster (S312). Operations S311 andS312 may have the same or different content according to the embodimentof the frame. The frame is received by the cluster header 11 inoperation S311 and it is transmitted to the network devices in itscluster in operation S312. The tracked device 102 receives the detectcall request frame and determines whether it allows location tracking(S314).

If location tracking is allowed, a detect call response frame includinglocation information is transmitted to the reference devices 401, 402and the cluster header 11 (S315). The reference device transmitspositioning data, which is obtained from information included in thereceived detect call response frame, to the cluster header 11 (S321). Asa result, the cluster header 11 becomes aware of the location of thetracked device 102 and it transmits a detect result frame to the PANcoordinator 31 (S331).

Also, in this situation the process can progress even without asking theuser of the tracked device whether he/she allows location tracking aspreviously described with reference to FIG. 3. Even if there is a denialresponse from the user, the detect call response frame can betransmitted to the PAN coordinator 31.

If a third device attempts to track the location of the tracked device102 through the PAN coordinator 31 or if the PAN coordinator 31 does notforce location tracking of the other device, the user of the trackeddevice 102 can prevent its location from being tracked. Here, thetracked device 102 transmits the detect call deny response frame to thereference devices 301, 302 and the cluster header 11 (S316). The clusterheader 11 transmits the received detect call deny response frame to thePAN coordinator 31 (S317) and the PAN coordinator 31 becomes aware thatthe tracked device cannot be tracked. Also, the detect call denyresponse frame can be transmitted to other devices that request thelocation of the tracked device 102.

FIG. 6 is a flowchart illustrating the process of device locationtracking using a relay device according to another exemplary embodimentof the present invention. The PAN coordinator may directly transmit thedetect call request to the cluster header or it may indirectly transmitit to the cluster header through another cluster header. Accordingly,the cluster header that receives and transmits the detect call requestframe functions as a relay device.

In FIG. 6, the PAN coordinator transmits the detect call request frameto the cluster header 51 (S411). The cluster header 51 transmits thedetect call request frame to a third cluster header 11 (S412) andcluster header 11 tracks the location of the device, which exists in itscluster. Here, different methods are performed depending on whether thetracked device allows or denies location tracking, as illustrated in theexamples of FIGS. 2 to 5.

When the tracked device allows its location to be tracked in operationS414, the cluster header 11 calculates position of tracked device inoperation S420, and tracks the location and transmits the detect resultframe to the cluster header 51 (S431), which also transmits the detectcall request frame (S432).

When the tracked device denies location tracking in operation S414, thecluster header 11 makes detect call deny response frame in operationS422, and transmits the detect call deny response frame (S434). Therelay device 51 that receives the detect call deny response frametransmits the detect call deny response frame to the PAN coordinator 31(S436).

There is various location tracking algorithms that can be used.

FIG. 7 is a concept diagram illustrating location tracking by a Time ofArrival (TOA) method according to an embodiment of the presentinvention. The TOA method measures the delivery time of the signals sentbetween the tracked device 101 and the other network devices 11, 301,302 in order to calculate the distance. The signal delivery time can beobtained by the difference between the transmission times of the frames(for example, the self detect initiation and the detect call response).By calculating this difference and knowing the speed of the signalcontaining the frame, three spherical ranges with the network devices11, 301, 302 as their centers are obtained. Three devices are requiredto perform the calculation of this method. If at least three referencedevices transmit the values, the coordinator 11 can select the threedata values that are judged to be the most accurate. In one embodiment,the accuracy of the data values can be judged by the received signalstrength. For example, Table 1, shown below, lists four devices 11, 301,302, 307 and the RSS and Positioning Data of signals sent by thesedevices. Since the device 307 of Table 1 has the weakest received signalstrength, it is disregarded (the positioning data from this device maybe inaccurate). TABLE 1 RSS Values and Positioning Data POSITIONING DATADEVICE RSS (m) 11 70 15 301 80 10 302 90 8 307 30 10

However, the received signal strength is exemplary, and the referencedevice may be determined according to the signal distortion or othercharacteristics of the signal.

FIG. 8 illustrates location tracking by the Time Difference of Arrival(TDOA) method according to an exemplary embodiment of the presentinvention. The TDOA method measures the difference between the arrivaltimes of two signals to determine the location, and it includes aforward link method composed of multiple signal sources and one receiverand a reverse link method composed of one signal source and multiplereceivers. The basic principle of TDOA is the signal arrival timedifference is proportional to the difference between the distances fromthe two signal sources to the receiver. These distances are calculatedand a receiver is chosen that is equidistant from the two signalsources, that is, a hyperbola centering on the two signal sources. Atthis time, each base station must be synchronized and the timesynchronization of the base stations is accomplished using a satelliteclock. Two hyperbolas are obtained from three signal sources and theintersection point of the two curves is the location of the receiver.

FIG. 8 shows the application of TDOA to IEEE 802.15.4. Here, theintersection of the hyperbola obtained from the network devices 11, 301and the hyperbola obtained from the network devices 11, 302 is thelocation of the tracked device 101. In order to obtain the intersectionpoint between the hyperbolas, the TOA data is transmitted to thecoordinator 11 by the reference network devices 301, 302. If thecoordinator 11 receives several signals, it can select a deviceaccording to RSS and calculate the positioning data.

In addition to the methods depicted in FIGS. 7 and 8, an Angle ofArrival (AOA) method and a Radio Frequency (RF) Finger Printer methodmay be used. The AOA method measures the incident angle of the framesignal transmitted from the tracked device and searches in thisdirection. In the present embodiment, the strongest signal can beselected among the values measured by several network devices.

The RF fingerprinting method takes a snapshot of the received signal,analyzes the snapshot and extracts a unique characteristic of thesignal, and compares this signal with the existing database to locatethe receiver in order to obtain a characteristic value of the frametransmitted by the tracked device.

The location tracking algorithms explained in the present specificationare only exemplary.

FIG. 9 illustrates a frame format of an MAC layer for embodying alocation tracking function according to an exemplary embodiment of thepresent invention. FIG. 9 illustrates one embodiment using the TOAalgorithm and may be changed according to the location tracking method.

The frame control of the IEEE 802.15.4 command frame 700 is 16-bits, andcontains the type of frame, an address field, and a control flag. Thesequence number is a unique identifier for the frame. The address fieldis composed of the PAN identifier/address field of the receiving sideand the PAN identifier/address field of the transmitting side. Thecommand frame identifier illustrates which command is being performedand can take the values shown in table 720. 0x0b to 0xff are reservedand may be defined in the future. Accordingly, location trackingcommands can be defined using these reserved identifiers.

The command payload is required to perform the command and can take thevalues shown in table 710.

The self detect initiation frame 711, which is transmitted when thetracked device wants to know its location, has the command frameidentifier 0x21, and corresponds to a command payload consisting of atracked device identifier and the frame transmission time. The otherreference devices (including the coordinator) that receive the frame cancalculate the distance using the frame transmission and reception time.This distance or the data is transmitted to the coordinator, therebyrevealing the location of the tracked device.

The calculated result is transmitted by the self detect result frame 712that has the command frame identifier 0x22 and a command payloadconsisting of the location information and the identifier of the trackeddevice.

Next, the structure of the detect call request frame 713, which is usedwhen the coordinator wants to know the location of a specific networkdevice, the detect call response frame 714 and the detect call denyresponse frame 717, which is transmitted in case of denying the locationtracking, will be described. The detect call request frame 713 is sentwhen searching for a tracked device that exists in the sender's networkand when searching for a reference device that does not exist in thesender's network. The command payload includes the identifier of thenetwork device being searched for. The tracked device, which receivesthe frame, transmits the detect call response frame 714 to disclose itslocation. The command payload included herein may be the identifier ofthe tracked device and the transmission time, as the self detectinitiation frame 711. On the other hand, when the tracked device denieslocation tracking, the detect call deny response frame 717 istransmitted. The command payload included herein may be the identifierof the tracked device.

The self detect initiation frame 711 and the detect call response frame714 include basic data for location tracking. When using the TOA methodor the TDOA method, the basic data may be the transmission time, andwhen using the RF fingerprinting method, the basic data may be thesignal strength. By combining the information, the location of thetracked device can be calculated. The positioning data frame 715 servesthe function of transmitting the calculated data to the coordinator. Thecalculated data may be the time difference between frame transmittingand receiving or it may be the distance information calculated from thetime difference information. Also, the calculated data may beinformation combining the incident angle of the signal and the distanceinformation. Further, the command payload may be the positioning data,which is calculated by the information included in the self detectinitiation frame 711 and the detect call response frame 714, the RSS,and the location of the reference device, which calculated the data. TheRSS is used in extracting the most reliable data when several networkdevices transmit the calculated data. Accordingly, the content of thepayload may vary according to the location tracking algorithm. Inaddition, the location information of the reference device is needed,because the calculated data is relative to the location of the referencedevice. If the coordinator of the network stores the locations of allthe devices that exist in its network, the location of the referencedevice need not be transmitted and can vary according to the embodimentof the coordinator.

The detect result frame 716 is used when the cluster header, to whichthe network device is associated, transmits the location information tothe PAN coordinator when the PAN coordinator, which requests thelocation tracking of a specific network device, exists in a PANdifferent from that of the network device. The cluster header transmitsthe command frame and payload, which includes the PAN identifier, theidentifier of the tracked device and the location information to the PANcoordinator.

The above-mentioned commands are one exemplary embodiment for embodyingthe location awareness, the detect result, the location awarenessrequest and the location information frame used in claims of the presentspecification. The self detect request frame 711 and the detect callresponse frame 714 are examples of the location awareness frame, and thedetect result frames 712, 716 are examples of the detect result frame.The detect call request frame 713 is an example of the locationawareness request frame and the positioning data frame 715 is an exampleof the location information frame.

The device identifier of the command, for example, the device identifierdefined by the detect call request frame 713 may include a pluralitypieces of the identifier information by various methods. That is, thedevice identifier may include the identifier of the device be tracked,and the identifier of the device that requests the location tracking. Inaddition, when searching for a device in another cluster, the identifierof the target cluster should be included in addition to the deviceidentifier.

FIGS. 10, 11, 12 are block diagrams illustrating command payloads of aframes according to an exemplary embodiment of the present invention.

FIG. 10 shows that the identifier information in the payload of thedetect call request frame varies according to conditions. In thesituation of FIG. 3, since the cluster header searches for the trackeddevice, frame 7131 consists only of the identifier of the trackeddevice. In the situation of FIG. 4, since the reference device searchesfor the tracked device, the frame 7132 includes the identifier of thedevice requesting the location tracking and the identifier of thetracked device. In the situations of FIGS. 5 and 6, since the devicebeing tracked exists in another cluster, frame 7133 is constructed toinclude the identifier of the device requesting the location tracking,the cluster identifier, and the identifier of the device which is theobject of the location tracking. To distinguish each frame, a check flagmay be included in the command frame.

FIG. 11 shows that the identifier information in the payload of thedetect call response frame varies according to conditions. Similar toFIG. 10, in the situation of FIG. 3, frame 7141 includes the identifierof the tracked device and the transmission time. In the situation ofFIG. 4, since the reference device searches for the tracked device,frame 7142 includes the identifier of the device requesting the locationtracking, the identifier of the tracked device, and the transmissiontime. In the situations of FIGS. 5 and 6, since the device being trackedexists in another cluster, frame 7143 includes the identifier of thedevice requesting the location tracking, the cluster identifier, theidentifier of the device being tracked and the transmission time. Todistinguish each frame, a check flag may be included in the commandframe.

FIG. 12 shows that the identifier information in the payload of thedetect call deny response frame varies according to conditions. 0x27 isthe identifier for the detect call deny response frame. The structure issimilar to that of the detect call response frame of FIG. 11, but itdoes not include information related to location tracking, such as thetransmission time, because location tracking has been denied. The detectcall deny response frame is the frame for notifying that the trackeddevice denies location tracking. In case of FIG. 3, the identifier 7151of the device which is the object of the location tracking but deniesthe location tracking is included. Frame 7152 is transmitted when thetracked device denies location tracking, as in the situation of FIG. 4,and includes the identifier of the device requesting location tracking,and the identifier of the device that is the object of the locationtracking. Frame 7153 is transmitted a device in another cluster requestslocation tracking, and it includes the cluster identifier of the clusterthat the requesting device resides in, the device identifier, and theidentifier of the device that is the object of the location tracking.

According to the present invention, the location of a device can betracked in a coordinator-based wireless network.

Particularly, a protocol that can perform location tracking in an IEEE802.15.4a environment is provided.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. The exemplary embodimentsshould be considered in a descriptive sense only and not for purposes oflimitation. Therefore, the scope of the invention is defined not by thedetailed description of the invention but by the appended claims, andall differences within the scope will be construed as being included inthe present invention.

1. A location tracking method in a coordinator-based wireless network,the method comprising: transmitting a first frame including anidentifier and time information to the wireless network by a deviceassociated with the wireless network in order to disclose locationinformation of the device; and receiving a response frame including thelocation information of the device transmitted from the wirelessnetwork.
 2. The method according to claim 1, wherein the wirelessnetwork uses IEEE 802.15.4 protocol.
 3. The method according to claim 1,wherein the time information is a transmission time of the first frame.4. The method according to claim 1, wherein the identifier is a mediumaccess control (MAC) address of the device.
 5. The method according toclaim 1, wherein the device is a device that requests a probe forverifying the existence of the wireless network, receives a proberesponse from the wireless network verifying the existence of thewireless network, requests to be associated with the wireless networkand receives an association response from the wireless network.
 6. Themethod according to claim 1, wherein the device is a device thatreceives a beacon from the wireless network verifying the existence ofthe wireless network, requests to be associated with the wirelessnetwork and receives an association response from the wireless network.7. A location tracking method in a coordinator-based wireless network,the method comprising: transmitting a first frame including identifiersof a first device and a second device to the wireless network so thatthe first device associated to the wireless network becomes aware of alocation of the second device; and receiving a response frame includinglocation information of the second device transmitted from the wirelessnetwork by the first device.
 8. The method according to claim 7, whereinthe wireless network uses IEEE 802.15.4 protocol.
 9. The methodaccording to claim 7, wherein the identifiers of the first and seconddevices are medium access control (MAC) addresses of the first andsecond devices, respectively.
 10. The method according to claim 7,wherein the first device is a device which requests a probe forverifying the existence of the wireless network, receives a proberesponse from the wireless network verifying the existence of thewireless network, requests to be associated with the wireless networkand receives an association response from the wireless network.
 11. Themethod according to claim 7, wherein the first device is a device whichreceives a beacon from the wireless network verifying the existence ofthe wireless network, requests to be associated with the wirelessnetwork and receives an association response from the wireless network.12. A location tracking method in a coordinator-based wireless network,the method comprising: receiving a first frame including an identifierof a first device which requests location tracking of a second deviceand an identifier of the second device from the wireless network by thesecond device; and transmitting a second frame including the identifierof the first device, the identifier of the second device and timeinformation of the second device to the wireless network by the seconddevice, as a response to the first frame.
 13. The method according toclaim 12, wherein the wireless network uses IEEE 802.15.4 protocol. 14.The method according to claim 12, wherein the identifiers of the firstand second devices are medium access control (MAC) addresses of thefirst and second devices, respectively.
 15. The method according toclaim 12, wherein the time information is a transmission time of thesecond frame.
 16. A location tracking method in a coordinator-basedwireless network, the method comprising: receiving a first frameincluding an identifier of a first device which requests locationtracking of a second device, and an identifier of the second device fromthe wireless network by the second device; determining whether locationtracking is allowed; and if location tracking is allowed, transmittingfrom the second device a second frame including the identifier of thefirst device, and the identifier and the time information of the seconddevice to the wireless network, as a response to the first frame. 17.The method according to claim 16, wherein the determining operationcomprises assessing an value inputted by the user of the second deviceallowed or denied location tracking.
 18. The method according to claim16, wherein the determining operation comprises determining by comparinga value which is previously set in the second device with the identifierof the first device.
 19. The method according to claim 16, wherein, whenit is found in the determining operation that location tracking isdenied, the second frame includes the identifier of the first device andthe identifier of the second device.
 20. The method according to claim16, wherein the wireless network uses IEEE 802.15.4 protocol.
 21. Themethod according to claim 16, wherein the identifiers of the first andsecond devices are medium access control (MAC) addresses of the firstand second devices, respectively.
 22. A location tracking method in acoordinator-based wireless network, the method comprising: receiving afirst frame including an identifier and time information of a devicetransmitted by the device; obtaining location calculating informationused in calculating a location of the device using the time information;and transmitting a second frame including the identifier of the deviceand the location calculating information to a network coordinator. 23.The method according to claim 22, wherein the wireless network uses IEEE802.15.4 protocol.
 24. The method according to claim 22, wherein thetime information is a transmission time of the first frame.
 25. Themethod according to claim 24, wherein the location calculatinginformation is a difference between reception time and transmission timeof the first frame.
 26. The method according to claim 22, wherein theidentifier of the device is a medium access control (MAC) address of thedevice.
 27. A location tracking method in a coordinator-based wirelessnetwork, the method comprising: receiving a first frame including anidentifier of a first device which requests location tracking of asecond device, and an identifier of a second device and time informationof the second device transmitted by the second device; obtaininglocation calculating information used in calculating a location of thesecond device using the time information; and transmitting a secondframe including the identifier of the first device, the identifier ofthe second device and the location calculating information to a networkcoordinator.
 28. The method according to claim 27, wherein the wirelessnetwork uses IEEE 802.15.4 protocol.
 29. The method according to claim27, wherein the time information is a transmission time of the firstframe.
 30. The method according to claim 29, wherein the locationcalculating information is a difference between reception time of thefirst frame and transmission time of the first frame.
 31. A locationtracking method in a coordinator-based wireless network, the methodcomprising: receiving a plurality of frames including an identifier of adevice and location calculating information of the device from thenetwork; calculating a location of the device using the locationcalculating information; and transmitting a frame including locationinformation to the device.
 32. The method according to claim 31, whereinthe wireless network uses IEEE 802.15.4 protocol.
 33. The methodaccording to claim 31, wherein the identifier of the device is a mediumaccess control (MAC) address of the device.
 34. A location trackingmethod in a coordinator-based wireless network, the method comprising:receiving a plurality of frames including an identifier of a firstdevice which requests location tracking of a second device, anidentifier of a second device and location calculating information ofthe second device from a network; calculating a location of the seconddevice using the location calculating information; and transmitting aframe including the location of the second device to the first device.35. The method according to claim 34, wherein the wireless network usesIEEE 802.15.4 protocol.
 36. The method according to claim 34, whereinthe identifiers of the first and second devices are medium accesscontrol (MAC) addresses of the first and second devices, respectively.37. A location tracking method in a coordinator-based wireless network,the method comprising: receiving a first frame including an identifierof a first device which requests location tracking of a second device,and an identifier of a second device from a network; transmitting thefirst frame to the second device of the network; receiving a secondframe which notifies that location tracking has been denied from thesecond device; and transmitting the second frame to the first device.38. The method according to claim 37, wherein the wireless network usesIEEE 802.15.4 protocol.
 39. The method according to claim 37, whereinthe identifiers of the first and second devices are medium accesscontrol (MAC) addresses of the first and second devices, respectively.40. A location tracking method in a coordinator-based wireless network,the method comprising: receiving a first frame including an identifierof a first device and an identifier of a second device transmitted bythe first device so that a coordinator of a first wireless network cantrack the second device; transmitting a second frame including anidentifier of the first wireless network, the identifier of the firstdevice and the identifier of the second device to a coordinator of asecond wireless network by the coordinator of the first wirelessnetwork; receiving a third frame including the identifier of the firstwireless network, the identifier of the first device, the identifier ofthe second device and location information of the second devicetransmitted by the coordinator of the second wireless network, by thecoordinator of the first wireless network, as a response to the secondframe; and transmitting a fourth frame including the locationinformation of the second device to the first device by the coordinatorof the first wireless network.
 41. The method according to claim 40,wherein the first and second wireless networks use IEEE 802.15.4protocol.
 42. The method according to claim 40, wherein the identifiersof the first and second devices are medium access control (MAC)addresses of the first and second devices, respectively.
 43. A locationtracking method in a coordinator-based wireless network, the methodcomprising: receiving a first frame including an identifier of a firstdevice and an identifier of a second device transmitted by the firstdevice so that a coordinator of a first wireless network can track thesecond device; transmitting a second frame including an identifier ofthe first wireless network, the identifier of the first device and theidentifier of the second device to a coordinator of a second wirelessnetwork by the coordinator of the first wireless network; receiving athird frame including the identifier of the first wireless network, theidentifier of the first device, the identifier of the second device bythe coordinator of the first wireless network, as a response of thesecond frame, if the second device which received the second framedenies location tracking; and transmitting a fourth frame includinginformation about the second device denying location tracking to thefirst device by the coordinator of the first wireless network.
 44. Themethod according to claim 43, wherein the first and second wirelessnetworks use IEEE 802.15.4 protocol.
 45. The method according to claim43, wherein the identifiers of the first and second devices are mediumaccess control (MAC) addresses of the first and second devices,respectively.
 46. A location tracking method in a coordinator-basedwireless network, the method comprising: receiving a first frameincluding an identifier of a first wireless network, an identifier of afirst device which requests location tracking of a second device, and anidentifier of a second device transmitted by a coordinator of the firstwireless network, by a coordinator of a second wireless network;transmitting a second frame including the identifier of the firstwireless network, the identifier of the first device and the identifierof the second device to the second device associated with the secondwireless network by the coordinator of the second wireless network;receiving a plurality of third frames including the identifier of thefirst wireless network, the identifier of the first device, theidentifier of the second device and location calculating information ofthe second device from the second wireless network by the coordinator ofthe second wireless network; calculating a location of the second deviceusing the location calculating information of the second device by thecoordinator of the second wireless network; and transmitting a fourthframe including the identifier of the first wireless network, theidentifier of the first device, the identifier of the second device andthe calculated location information of the second device to thecoordinator of the first wireless network by the coordinator of thesecond wireless network.
 47. The method according to claim 46, whereinthe first and second wireless networks use IEEE 802.15.4 protocol. 48.The method according to claim 46, wherein the identifiers of the firstand second devices are medium access control (MAC) addresses of thefirst and second devices, respectively.
 49. A location tracking methodin a coordinator-based wireless network, the method comprising:receiving a first frame including an identifier of a first wirelessnetwork, an identifier of a first device which requests locationtracking of a second device, and an identifier of a second devicetransmitted by a coordinator of the first wireless network; transmittinga second frame including the identifier of the first wireless network,the identifier of the first device and the identifier of the seconddevice to a coordinator of a third wireless network by a coordinator ofthe second wireless network; receiving a third frame including theidentifier of the first wireless network, the identifier of the firstdevice, the identifier of the second device and location information ofthe second device transmitted by the third wireless network, by thecoordinator of the second wireless network; and transmitting a fourthframe including the identifier of the first wireless network, theidentifier of the first device, the identifier of the second device andthe location information of the second device to the coordinator of thefirst wireless network by the coordinator of a second wireless network.50. The method according to claim 49, wherein the first, second andthird wireless networks use IEEE 802.15.4 protocol.
 51. The methodaccording to claim 49, wherein the identifiers of the first and seconddevices are medium access control (MAC) addresses of the first andsecond devices, respectively.